As hinted at by @sumelic, in a comment above, the use of indolent as you have defined it (and as it seems to be defined in a number of dictionaries) is unusual outside of the medical sense. Consider:
indolent adjective Medspeak Referring to a condition that may linger
longer, but often slowly progresses to a more advanced stage—e.g.,
indolent lymphoma, indolent malignancy, indolent myeloma.
Vox populi Slow growing.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.
in·do·lent (in'dō-lent), Inactive; sluggish; painless or nearly so,
said of a morbid process. [L. in- neg. + doleo, pr. p. dolens (-ent-), to feel pain] Farlex Partner Medical Dictionary © Farlex 2012
Lymphomas are commonly also categorized as indolent or aggressive.
Indolent lymphomas are slowly progressive and responsive to therapy
but are not curable with standard approaches. Aggressive lymphomas are
rapidly progressive but responsive to therapy and often curable.
From a search for indolent in the Merck manual.
These are examples of the use of indolent as a fairly narrowly defined adjectival descriptor of a growth, tumour or other malignancy.
Your question might be best answered by aggressive being the opposite of indolent in a medical sense. Whether this necessarily means painful is moot.
Physicians often use exquisite pain to describe intense pain. This may answer part of the pain question.